Pay per prompt.
No signup.
Sign once,
get any model.
A drop-in OpenAI-compatible API for 43 frontier models — Claude, GPT-5.5, Gemini 3.1, Grok, Veo, Kling, nano-banana — settled in USDC over x402. No accounts. No invoices. Just an HTTP 402 and a signature.
# 1. quotecurl -sX POST https://api.x402prompt.com/v1/chat/completions \-H "Content-Type: application/json" \-d '{"model":"claude-opus-4-7","messages":[{"role":"user","content":"hi"}],"max_tokens":50}'# ← HTTP/1.1 402 Payment Required# PAYMENT-REQUIRED: <base64 quote · 0.150000 USDC · base># 2. sign & retrycurl -sX POST https://api.x402prompt.com/v1/chat/completions \-H "Content-Type: application/json" \-H "PAYMENT-SIGNATURE: <base64 eip-3009 transferWithAuthorization>" \-d '{"model":"claude-opus-4-7","messages":[{"role":"user","content":"hi"}],"max_tokens":50}'# ← HTTP/1.1 200 OK# PAYMENT-RESPONSE: <base64 settled · tx 0x058519e8…7e89794># {"choices":[{"message":{"content":"Hello! How can I assist you today?"}}],...}
Token-accurate on prepaid. Flat ceiling on PAYG.
Prepaid bills chat per actual prompt + completion tokens (reserve-max → finalize-actual → refund-excess). PAYG quotes one flat per-call price upfront. Image and video are per-call in both modes. Numbers below are the PAYG quote — also the upper bound on prepaid.
Two flows. Both end in a signature.
Sign per request.
Send a request without auth. Our server quotes a flat price per model. Sign EIP-3009 once per call. Useful for agents that don't maintain state or for one-off generations.
- 01POST /v1/chat/completions→ 402 + quote
- 02wallet.signTypedData(...)TransferWithAuthorization
- 03POST again with PAYMENT-SIGNATURE→ 200 + completion
Top up, get a key.
One x402 payment credits a balance keyed to your wallet. Receive a bearer api key. Subsequent calls debit at token-accurate rates with refund on client disconnect.
- 01POST /v1/topup?amount=5sign once · receive key
- 02Authorization: Bearer sk-x402-…reserve max
- 03finalize actual → refund deltabalance auto-tracked